This invention relates to bituminous roofing adapted for the waterproofing and sealing of substrate structures and to the method of manufacturing such materials. More particularly, the present invention is in the field of roofing membranes having a factory-applied self-adhesive layer on the bottom surface and a thermoplastic modifier such as Atactic PolyPropylene (APP) modified bituminous compound or an elastomeric modifier such as Styrene-Butadiene-Styrene (SBS) modified bituminous compound on the upper surface, and an adhesive coating on the overlap sections of the weathering (upper) surface of modified bitumen roofing membranes to which the underside of a succeeding sheet of membrane may be adhered in order to provide good sealability in addition to easy and hassle-free field application by roofing personnel.
It is well known to use bituminous compositions for manufacturing waterproofing membranes, generally for roof covering and roofing underlayments. Modified bituminous prepared roofing, also referred to as modified asphalt roofing membrane, is typically manufactured using, as a core, a reinforcement carrier support sheet made of fabric such as polyester, fiberglass, or a combination of both, saturating and coating the front and back sides of the carrier with a modified bituminous coating material based on Atactic PolyPropylene (APP), Amorphous Poly Alpha Olefin (APAO), Thermoplastic PolyOlefin (TPO), Styrene-Butadiene-Styrene (SBS), Styrene-Ethylene-Butadiene-Styrene (SEBS), synthetic rubber or other asphaltic modifiers, that will enhance the properties of asphalt.
Of the two most common types of bituminous sheet materials used for roofing applications, i.e., bitumen-SBS and bitumen-APP materials, the bitumen-SBS products are more elastic, have greater flexibility at low temperatures. APP-based products, however, are more heat-resistant (due to a higher softening point), are more resistant against the effects of the atmosphere (especially ultra-violet rays) and more resistant to foot traffic.
Whereas APP modified roofing membranes are usually torched and SBS modified roofing membranes are usually hot mopped, there exists another class of membranes called “self-adhered”, that are based on APP or SBS. These membranes are generally made using dual compound technology-APP or SBS compound on the top surface and a self-adhesive compound on the bottom surface. The manufacture of bituminous roofing material with multiple layers is well-known. For example, U.S. Pat. Nos. 2,893,889; 4,755,409; 4,871,605; and EP Patent No. 903435 disclose membranes comprised of a core and a plurality of different layers of waterproofing material. The '409 patent also discloses a release sheet applied to the one side of the membrane for purposes of protection. Products are in the market which combine the more flexible and elastic bitumen-SBS upper layer with a self-adhesive lower surface. An example of such a product is Plura AD self-adhesive sold by Pluvitec S.p.A., described on the website of the seller at http://www.pluvitec.com. Furthermore, it is known in the prior art to join two roofing membranes in order to effect sufficient sealing and waterproofing. For example, U.S. Pat. No. 6,360,506, discloses a membrane containing two bitumen strips used for joining two separate roofing membranes.
In applications in which more than one course of the membrane is applied to the roof deck or underlayment, adjacent rolls need to be adhered to each other by overlapping in offset pattern at the end laps (widthwise) and at side laps (lengthwise). If employed, these laps must be watertight and also possess a high degree of structural integrity. Of course, if an effective seal is not attained, the membrane system will leak and therefore, not achieve its very purpose. It is a known fact that the weakest points on a continuous roof are the lap joints. Whereas these laps are sealed by heat welding in the case of torch-grade products and using hot asphalt in hot-mopped products, lap seal for membranes in this invention is achieved by sticking the self-adhesive compound to the upper surface of the membrane. This seal is immediate and becomes irreversible when activated by heat and pressure.
As part of the present invention a pressure sensitive adhesive is preferably applied on the overlap areas, namely the end lap and side lap, of the roofing membrane in order to provide an instantaneous bonding between the two surface layers and to improve the bonding strength especially in cold weather conditions. The adhesive layer is applied on the upwardly facing selvage edge (i.e., the side lap) along the length of the sheet with the adhesive preferably, but not necessarily, spaced inwardly of the outermost edge. The adhesive layer is similarly applied on the upwardly facing trailing edge portion of the upper layer (i.e., the end lap) across the width of the sheet. The adhesive on the upwardly facing portion of the end lap is protected using a 4 to 6 inch wide siliconized film and the adhesive on the side lap is protected using a 3 to 4 inch wide siliconized film. In use, when the membrane is secured to the roof, the leading edge of a new roll in a row is placed onto the end lap of a previously laid roll in that row after removal of the release liner. The upper layer with the upwardly facing adhesive edges constitutes a starter strip for receiving thereon the adjacent rolls of roofing membranes. Similarly, when forming a new row, a release liner is removed from the side lap of the rolls in an existing row of membranes, and the self-adhesive underside of a new roll is placed on the adhesive-bearing portions of the previously laid rolls, i.e., the edges exposed by the removal of the release liner. Within the above-described scope the goal of the invention is to provide membranes that are impermeably sealed to adjacent or contiguous membranes in an effective and aesthetically pleasing manner. The membrane that is the subject of this invention provides a reliable seal between membranes because of its unique design features. The subject bitumen based membrane is easy to produce because it is made of elements and materials that are available on the market. Further, the membrane of the present invention is relatively inexpensive to manufacture and install.
This invention is preferably implemented by using a “dual compound” to the reinforcement carrier sheet—a compound based on Atactic PolyPropylene (APP), Amorphous Poly Alpha Olefin (APAO), Thermoplastic PolyOlefin (TPO), Styrene-Butadiene-Styrene (SBS), Styrene-Ethylene-Butadiene-Styrene (SEBS), synthetic rubber or other asphaltic modifiers on the top surface, and a separate heat-and-pressure-activated adhesive compound to the bottom surface of the reinforcement carrier sheet. The membranes in this invention are characterized by the fact that they include an end lap and a side lap, which consist of a tract of exposed bitumen, free of granular material with an adhesive strip on the end laps and side laps of the upper surface of the membrane to facilitate easy and excellent adhesion. This invention applies to self-adhesive membranes based on dual-compounding technology that constitute cap sheets such as APP modified and SBS modified, base sheets such as APP modified and SBS modified, and underlayments such as employed under tile roofing and metal panels.
APP modified compound utilized on the upper layer offers plastomeric characteristics to the bitumen and makes the membrane hard and imparts improved flow resistance at high temperatures. A release liner, typically made of polypropylene, polyethylene or polyester, of thickness ranging from 40 to 80 microns, and treated with a silicone adhesive on one side (the side that comes in contact with the self-adhesive compound), is applied to the self-adhesive compound to prevent sticking of adjacent sections of the roofing material and to the packaging when the finished membrane is stored and transported in the form of rolls.
The present invention involves roof coverings in the form of roofing membranes having an upper layer of a modified bituminous compound, whose composition utilizes bitumen (asphalt), modifiers and fillers, and a lower layer of a self-adhesive compound, whose composition utilizes bitumen (asphalt), elastomeric modifiers, tackifying resins, and fillers. A typical APP compound may contain 5% to 25% of polypropylene modifiers, 8% to 70% of filler such as limestone, talc, fly ash, volcanic ash, graphite, carbon black, silica or china clay, and remaining portions of asphalt. In order to achieve fire ratings as classified by Underwriters' Laboratories (UL), special fire retardant additives may be used as filler. A typical SBS compound may contain 4% to 16% of Styrene-Butadiene-Styrene modifiers, 8% to 70% of filler such as limestone, talc, fly ash, volcanic ash, graphite, carbon black, silica or china clay, and remaining portions of asphalt. In order to achieve fire ratings as classified by Underwriters' Laboratories (UL), special fire retardant additives may be used as filler. A typical self-adhesive compound may contain 3% to 10% of Styrene-Butadiene-Styrene modifiers, 0% to 5% of Styrene-isoprene-styrene modifiers, 6% to 25% of hydrocarbon tackifying resins, 8% to 40% of filler such as limestone, talc, fly ash, volcanic ash, graphite, carbon black, silica or china clay, and remaining portions of asphalt.
The inventive membrane has a carrier that supports a dual compound modified asphalt, namely, an APP modified or SBS modified asphaltic compound, which is positioned on top of the carrier sheet, and a self-adhesive modified asphaltic compound, which is positioned below the carrier sheet. The adherent material serves to affix the membrane to the roof deck, base sheet or underlayment.
In order to provide adhesion and a watertight seal between the self-adhesive compound on the lower surface of the membrane and the modified bitumen compound on the upper surface, an adhesive that is compatible with both the modified bituminous coating layers must be utilized on the overlap areas. For this purpose, the adhesive selected should be compatible with the self-adhesive compound utilized on the back surface of the membrane
One choice for adhesive could be the self-adhesive compound applied on the back side of the membrane. Alternatively, tackifiers such as Poly Vinyl Butyral (PVB) used in formulating the self-adhesive compound can be used. PVB is primarily used as an interlayer between car windshield glass. Use of PVB helps reduce the possibility of ‘shattering of glass’ in the case of accidents and also provides good sound dampening properties. Each year, millions of pounds of PVB are discarded after use. Monsanto is one company that has perfected a process of removing the car windshield glass so that they could preserve the PVB layer sandwiched between the glass layers. Other choices for this application are Pressure sensitive adhesives (PSA) that are commercially available. PSAs are based on silicones, rubber or acrylates. For this application a Styrene-Isoprene-Styrene (SIS) rubber based adhesive is preferred because of its superior low temperature tack and low cost. PSA selected for this use is manufactured and sold by Forbo Adhesives (formerly Reichhold Corporation), Research Triangle Park, N.C., under the trade name of PSA 81570. These adhesives have excellent tack properties at low temperatures, which is very critical for this application. These are fast setting adhesives, designed for good performance and good machining at high production speeds. This PSA is used for both APP based and SBS based modified bituminous membranes.
Using an adhesive applicator, typically 2-3 strips of adhesive are applied on the lap areas in the form of swirls that are 0.5 inch to 1.5 inch in width each. In order to achieve good bonding between adjacent layers, a minimum of 40 grams of adhesive per 10-meter long roll is preferred. This pressure sensitive adhesive provides excellent surface tack as well as adequate strength for use in self-adhered roofing application.